Antihalation layer for cellulose ester lithographic printing plates



y 13, 1952 e. F. NADEAU ET AL 2,596,713

ANTIHALATION LAYER FOR CELLULOSE ESTER LITHOGRAPHIC PRINTING PLATES Filed Feb. 9, 1949 FIG. 1.

H CELLULOJE ACETATE ANT/HALAT/ON DYE LAYER .FIG.2.

SENS/7725p H YDROL HE D JUKFA CE k CELLULOSE ACETATE A DHES I VE CELLULOJE ACEMTE GALE F. MDEAU CLEiENS B STARCK IN V EN TORS BY J My," MWQMM ATTORNEY & AGENT Patented May 13, 1952 UNITED ANTEHALATION LAYER FOR CELLULOSE ESTER LITHOGRAPHIC P R I N T I N G PLATES Gale F. Nadeau and Clemens B. Starck, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application February 9, 1949, Serial No. 75,444

4 Claims. 1

This invention relates to the preparation of light-sensitive photographic elements protected against halation and particularly designed for use in making lithographic printing plates.

Printing plates of the lithographic type are well known having previously been prepared, for example, from metal plates carrying sensitive colloid layers and from cellulose ester plates carryme a sensitive stratum or layer. In processes of making such plates, as in many photographic processes utilizing light-sensitive layers, in order to avoid halation effects, it is desirable to provide the sensitive element with an antihalation layer which absorbs rays of light transmitted by the sensitive layer in order to prevent their reflection back to the sensitive layer. The Colt U. S. Patent 2,448,861, granted September 7, 1948, describes a method for the preparation of cellulose ester printing plates according to which a hydrolyzed surface layer of a cellulose ester sheet is sensitized with bichromate and after exposure under a design the exposed area is removed with solutions of chlorites or hypochlorites, thereby providing ink-receptive areas in the region of the exposure and the remaining areas of the element are ink-repellent when it is moistened. In this process, it is also highly desirable to provide the sensitive printing plate with an antihalation of the desired characteristics such as thickness;

layer, and, following the usual practice in the art it might appear that the antihalation layer might be coated on the rear surface of the sensitive plate. However, it has been found that when such elements are subjected to alkaline hydrolysis by simple immersion methods to produce a stratum of hydrolyzed cellulose ester on the surface of the plate, the dye of the antihalation layer is released into the hydrolyzing bath resulting on the one hand in a loss of antihalation dye density and on the other hand, the dye released colors the hydrolyzed surface and as a result of the filter effect of the dye, considerable loss in sensitivity of the product results.

We have discovered that the antihalation layer may be protected against the efiects of the hydrolyzin baths and similar influences by incorporating it into the support for the cellulose ester printing plate.

One object of our invention is to provide a sensitive element protected against halation for use in making lithographic printing plates. Another object is to provide a lithographic printil'lg plate having an antihalation layer protected against deleterious effects of chemical baths. A further object is to provide a novel process of preparing a printing plate protected against halaadhesion, or resistance to caustic alkali, to accomplish the desired result, and further, a more costly product would result. In the latter case were the dye to be dispersed uniformly in the support, the same original difiiculties result since the dye is leached from the support by the caustic hydrolyzing solution reducing the amount of antihalation dye available and the leached dye stains the sensitive surface as described.

Our invention will be understood by consideration of the following illustrative examples and I the drawings which show in enlarged cross-sectional view in Fig. l the laminated support and in Fig. 2 the sensitized laminated plate protected against halation and which is used in making lithographic printing plates.

Example A clear sheet of cellulose acetate film 0.003-inch thick is coated on one side with a solution of a blue-absorbing dye such as a dye disclosed in Dickey U. S. Patent 2,264,303, granted December 2, 1941, particularly p-nitrobenzene-azo-N(fi-hydroxylethyl)o-chloro aniline. The preferred dye is used in a three per cent solution of a mixture of 10 per cent fi-methoxy ethanol, per cent acetone and 40 per cent methanol. After coa ing and drying the sheet, it is laminated with the dyed surface toward a second sheet of clear cellulose ester bringing the two sheets between pressure rollers with a head of cement between. A suitable cement consists of a two per cent dope of cellulose triacetate in a mixture of per cent methylene dichloride, 5 per cent ethylene dichloride and 15 per cent methanol. The product is then dried to remove the solvents and is ready for use in making a printing plate. If desired, the dye density may conveniently be increased by laminatin the surface dyed sheet to the dyed surface of a second similarly dyed sheet. This is sometimes preferred when unusually high dye densities are required. The laminated element appears as shown in Fig. 1 of the accompanying drawings wherein cellulose acetate layers l and H are cemented together with adhesive layer [2 and the antihalation dye layer I3 is contiguous to the lamination interface.

The laminated support prepared according to Example 1 is surface-hydrolyzed on one or both surfaces by treatment with an alcoholic caustic alkali solution by immersion or coating methods for the time and under the condition producing hydrolysis to the required depth. Ordinarily, the thickness of the hydrolyzed stratum is of the order of one micron. After surface hydrolysis is complete, the film is washed, excess alkali neutralized with dilute acid solution and then the element is washed and dried. The film is then sensitized with sensitizing agents such as chromium, iron or uranium salts, for example, potassium dichromate, ferric chloride, or ferric ammonium oxalate plus ferricyanide, as disclosed in the pending Kenyon and Unruh Application Serial No. 75,453, now Patent No. 2,548,537 of April 10, 1951, and Kenyon and Cathcart Application Serial No. 75,452, now Patent No. 2,568,503 of Sept. 18, 1951, both filed concurrently with this application. These sensitizing agents include sensitizers which, like bichromate, will quickly oxidize hydrolyzed cellulose ester in the presence of ultraviolet light transmitted by a design, to an alkali-soluble state, and include other sensitizers such as ferric ammonium oxalate which is reducible to ferrous salt images in the presence of light but which sensitizer does not oxidize cellulose in the presence of light, consequently alkalin-oxidizing solutions must be used to effect removal of the hydrolyzed cellulose ester in the exposed area.

The sensitized hydrolyzed element of our invention is shown in Fig. 2 of the drawings wherein the cellulose acetate layers and H are adhered together by means of adhesive layer I2, the antihalation layer 13 disposed as shown and the outer stratum l4 of layer I l is hydrolyzed and sensitized as shown.

Exposure and processing of the sensitized element is carried out according to any of the methods of the above pending inventions or the plate may be processed by the method of the Colt patent. According to those processes, the exposed area of the hydrolyzed cellulose ester stratum is oxidized and rendered soluble in alkalin solutions. Treatment with an alkali solution then removes the oxidized cellulose ester in the exposed area baring the underlying inkreceptive cellulose ester printing areas, while the unexposed areas are ink-repellent when the surface is moistened as usual in a lithographic press.

The antihalation layer of the invention may be disposed in the manner described between layers of cellulose ester such as substantially fully esterified cellulose triacetate having the maximum resistance to moisture and containing about 43.5% acetyl, and in addition, other cellulose esters such as cellulose acetate propionate, or cellulose propionate having equivalent properties and acyl content may be used in the same manner but are less preferred. The sheet to be laminated may be of thickness of the order of .003-.005 inch yielding laminated products as thick as 0.01-inch. Another advantage of incorporating the antihalation stratum into a laminated element will be apparent to those skilled in the art of coating colloid layers. That is, it is extremely diflicult to coat and properly cure layers of thickness of the order of .01-inch in a single operation and in those cases where plates of this thickness are required, it is for tuitous that the lamination procedure produces two results, the one being the sealing of the dye into the support and the other the provision of a thick support.

Our invention having been described, it is to be understood that the disclosure herein is by way of example and our invention is to be limited only by the scope of the appended claims.

What we claim is:

1. A light-sensitive photographic element designed for use in preparing a lithographic printing plate, comprising two sheets of substantially fully esterified cellulose organic acid ester each from about .003 to about .005 in. thick and laminated together, and antihalation dye layer contiguous to the lamination interface, and on one of the outer surfaces of one of said sheets a stratum of hydrolyzed cellulose ester uniformly sensitized to light with a compound selected from the class consisting of oxidants for the hydrolyzed cellulose ester in the presence of light and lightreducible ferric salts incapable of direct oxidation of the hydrolyzed cellulose ester to the alkali soluble state in the presence of light.

2. A light-sensitive photographic element designed for use in preparing a lithographic printing plate, comprising two sheets of substantially fully esterified cellulose organic acid ester each from about .003 to about .005 in. thick and laminated together, an antihalation dye layer contiguous to the lamination interface, and on one of the outer surfaces of one of said sheets a stratum of hydrolyzed cellulose ester uniformly sensitized to light with bichromate.

3. A light-sensitive photographic element designed for use in preparing a lithographic printing plate, comprising two sheets of substantially fully esterified cellulose organic acid ester each from about .003 to about .005 in. thick and laminated together, an antihalation dye layer contiguous to the lamination interface, and on one of the outer surfaces of one of said sheets a stratum of hydrolyzed cellulose ester uniformly sensitized to light with a ferric salt oxidant for the hydrolyzed cellulose ester.

4. A light-sensitive photographic element designed for use in preparing a lithographic printing plate, comprising two sheets of substantially fully esterified cellulose organic acid ester each from about .003 to about .005 in. thick and laminated together, an antihalation dye layer contiguous to the lamination interface, and on one of the outer surfaces of one of said sheets a stratum of hydrolyzed cellulose ester uniformly sensitized to light with a ferric ammonium salt of an organic acid.

GALE F. NADEAU.

CLEMENS B. STARCK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,908,527 McMaster May 9, 1933 1,943,486 Ostwald Jan. 16, 1934 2,305,169 Lierg Dec. 15, 1942 FOREIGN PATENTS Number Country Date 337,868 Great Britain -1 Nov. 13, 1930 394,298 Great Britain Publ. 1933 

1. A LIGHT-SENSITIVE PHOTOGRAPHIC ELEMENT DESIGNED FOR USE IN PREPARING A LITHORGRAPHIC PRINTING PLATE, COMPRISING TWO SHEETS OF SUBSTANTIALLY FULLY ESTERIFIED CELLULOSE ORGANIC ACID ESTER EACH FROM ABOUT .003 TO ABOUT .005 IN THICK AND LAMINATED TOGETHER, AND ANTIHALATION DYE LAYER CONTIGUOUS TO THE LAMINATION INTERFACE, AND ON ONE OF THE OUTER SURFACES OF ONE OF SAID SHEETS A STRATUM OF HYDROLYZED CELLULOSE ESTER UNIFORMLY SENSITIZED TO LIGHT WITH A COMPOUND SELECTED FROM THE CLASS CONSISTING OF OXIDANTS FOR THE HYDROLYZED CELLULOSE ESTER IN THE PRESENCE OF LIGHT AND LIGHTREDUCIBLE FERRIC SALTS INCAPABLE OF DIRECT OXIDATION OF THE HYDROLYZED CELLULOSE ESTER TO THE ALKALI SOLUBLE STATE IN THE PRESENCE OF LIGHT. 